makefile: Add READELF command variable

This allows setting READELF=llvm-readelf in order to use the LLVM
version of the readelf utility. It also aligns with the practice of not
using $(CROSS_COMPILE) in any build recipes directly, reducing the
number of places where $(CROSS_COMPILE) is used.

Signed-off-by: Sam Edwards <CFSworks@gmail.com>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
1 file changed